This invention relates to a wafer probe with a transparent loading member.
An important aspect of the manufacture of integrated circuit chips is the testing of the circuit embodied in the chip in order to verify that it operates according to specifications. Although the circuit could be tested after the chip has been packaged, the expense involved in dicing the wafer and packaging the individual chips makes it desirable to test the integrated circuit as early as possible in the fabrication process, so that unnecessary efforts will not be expended on faulty devices. It is therefore desirable that these circuits be tested after wafer fabrication is completed, and before separation into dies. In either case, it is necessary to make electrical connection to connection elements of the circuit in a non-destructive fashion, so as not to interfere with subsequent packaging and connection operations.
Generally, integrated circuit chips are rectangular and the connection elements are distributed around the periphery of one main face of the die. The connection elements are generally in the form of flat connection pads, but it is known to employ connection elements in the form of bumps, which may be hemispherical in form.
A conventional testing station for testing integrated circuits in wafer form comprises a vacuum chuck and a probe support. The vacuum chuck is positioned on a rigid base structure, and the probe support is located at a predetermined height above the base structure. The vacuum chuck includes a platform on which a wafer composed of integrated circuits to be tested is placed. The probe support is fixed against movement relative to the base structure, but the chuck is movable linearly along two perpendicular horizontal axes relative to the base structure (X and Y axis movement) and is rotatable about a vertical axis (theta movement), and the platform can be raised or lowered (Z axis movement). A wafer probe is carried by the probe support and has contact elements for engaging connection elements of a die under test (DUT). The contact elements of the wafer probe are generally hemispherical bumps if the connection elements of the die are flat pads and are contact pads if the connection elements of the die are hemispherical bumps. By displacing the chuck horizontally, the DUT can be positioned so that its connection elements are vertically below the contact elements of the probe and by raising the platform the connection elements of the die can be brought into contact with the contact elements of the probe.
It is important that the DUT be accurately positioned in the X-Y plane relative to the contact elements of the probe, so that the contact elements of the probe are engaged by the connection elements of the DUT when the wafer is raised by the vacuum chuck. Furthermore, in order to provide consistent test results it is necessary that the contact force between the connection elements of the die and the respective contact elements of the probe be substantially the same from die to die and from wafer to wafer.
Generally, it is only necessary to position one die of a wafer relative to the probe, because the relative positions of the dies on the wafer are accurately known and once the probe has been accurately positioned relative to one die, it can readily step to each of the other dies without operator intervention.
U.S. Pat. No. 4,912,399 issued Mar. 27, 1990 discloses a wafer probe that comprises a transparent flexible membrane. An operator can view the die on the vacuum chuck through the membrane and can insure that the contact elements of the probe are properly positioned relative to the connection elements of the die before the vacuum chuck is raised. Contact pressure is provided by a rigid pressure plate that extends over the membrane and resilient material between the membrane and the pressure plate.
U.S. Pat. No. 4,891,585 issued Jan. 2, 1990 discloses a wafer probe comprising a circuit board that spans an opening in the probe support and a transparent flexible membrane that spans an opening in the circuit board. Upward movement of the contact area of the membrane is limited in resiliently yieldable fashion by a back-up structure that comprises a hard pressure pad engaging the membrane, a rod of elastomer material and a plate that is secured to the probe support. The back-up structure is transparent, allowing an operator to view the contact elements of the probe and the connection elements of the die to be tested through the backup structure and the membrane.
U.S. Pat. No. 4,758,785 issued July 19, 1988 discloses a test station in which upward deflection of the flexible membrane is resisted by a metal spring that bears against the flexible membrane through a transparent pressure pad. The pressure pad carries the movable contact of a switch that controls vertical movement of the vacuum chuck. The stationary contact of the switch is mounted on the probe support. When the contact elements of the membrane are spaced from the connection elements of the die under test, the metal spring, acting through the pressure pad, deflects the membrane downwards and the movable contact of the switch engages the stationary contact. When force is applied to the contact elements of the probe such as to deflect the membrane upwards, this force is resisted in resiliently yieldable fashion by the metal spring. When the membrane has been deflected upwards by a predetermined amount, the movable contact of the switch leaves contact with the fixed contact and further upward movement of the vacuum chuck is prevented.
Publication no. EPA-A2-0,259,163 discloses a wafer probe that is similar in many respects to that shown in U.S. Pat. No. 4,758,785.
Publication No. EPA-A1-0,131,375 discloses a wafer probe in which probe supports, which are attached to a probe board, carry conductive probe elements for probing an integrated circuit die in wafer form.